Wood materials which are processed to panels are generally surface-coated. It is only the surface coating that gives rise to the actual utility of the panels, since it imparts decorative properties, water resistance, abrasion resistance, chemical resistance, if appropriate resistance toward algae, fungi and/or insects. The surface coating is typically effected by a coating of the panel with a synthetic resin-impregnated decorative paper.
Alternatives to coating with decorative paper have been described, for example in AT 351 744, but these coatings have not become established in practice. AT 351 744 describes the varnishing of a chipboard, a first varnish application being referred to as priming. The primer is applied on both surfaces, top side and bottom side of the chipboard. A second varnish application follows. The second varnish layer is applied on one side, only to the top side of the chipboard. The varnish application is from at least 50 to 500 g/m2. The process proposed here dispenses with decorative paper. The aim is the saving of expensive plant parts such as presses. However, the synthetic resin proposed here predominantly for the varnish layers is melamine, one of the most expensive varnish components. The product proposed in AT 351 744 has not become established in industry, for reasons including cost. The application of the varnish has also been found to be problematic, since it was considered to be necessary to apply thick varnish coats on the assumption that an appropriate, maximum layer thickness is required to achieve the desired durability. However, the application and curing of thick varnish layers is technically complicated and hence costly.
The application of visually satisfactory varnish layers has to date entailed the provision of abrasive layers in the varnish structure, which, after the application and curing of a first varnish layer, cover this first varnish layer. The abrasive layers are in each case sanded off again largely or completely in order to obtain a smooth substrate for the next varnish layer. This multilayer method with intermediate sanding is required to obtain visually appealing varnish layers.
The application of UV-curable varnishes provides a remedy here. One example of the use of UV-curable varnishes is shown by U.S. Pat. No. 4,439,480.